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The F/A-18 Hornet , F15 and MiG-29 ailerons from the external parts of the wings go up some degrees in flight ,meaning adding " crow" .Why?
In some parts of the flying envelope of the F/A-18 Hornet and MiG-29  the ailerons from the external parts of the wings go up in sync. They're made to go one up one down in order to get rolls, not up/up .

https://m.facebook.com/story.php?story_fbid=548605942390983&id=148530445855064

It may be (with staticly unstable set up) to neutralize static stability or even help with pitching control.  When ailerons move in unison, in one direction, they become elevators, hence the term elevons.

It is wrong to assume any flight control surface on a modern fighter jet would have a simple traditional function. (They're made for swing up /down in order to get rolls, not up /up). The flight control computer can use any surface for any desired effect if it is programmed to do so.

Mig 29 is not fly by wire jet

Doesn't have to be fly-by-wire to have a flight control computer that can add the sort of other-that-traditional inputs  that Jpe61 mentions into a mix that directs hydraulic controls. Lots of non-FBW aircraft have inputs (stick pusher, speed trim, yaw damper, etc) into their flight controls from sources other than the pilot.

Ha, you got me there @GeorgeGeo! It is hydraulic however, so some logic might be intervening the movement of flight control surfaces.

BTW I don't see why this question would deserve minus points? It is a valid question, and I'm sure someone (not me though) will be able to give at least a theoretical reason for the fcs movements.

Are we sure this isn't just an optical illusion due to a slight flap deflection downward during maneuvering?

Bryson S , I looked at many videos of these two aircrafts so I'm sure .

It might also be some kind of negative flap function (as used on gliders at high speed).

Manu H It's very good example

@GeorgeGeo now that you've added the bounty you might wan't to rephrase the question a little, because it is clear that the MiG-29 ailerons only move to roll the plane. G -force has no effect.

What does the term "add crow" mean, and what does it bring to the question?

What is an "add crow" type of winglet? It may be better to ask a whole new question instead of editing this old one with a bunch of existing answers.

@Michael Hall ;maybe someone here want to learn the term.That's it .

The pictures in the question show the normal position of the MiG-29 ailerons. That's how they are unless a roll is commanded.
According to Mikoyan Mig-29 Fulcrum Pilot's Flight Operating Manual (google books) the slight upward position is set to improve yaw stability during roll meneuvers:

As for whether this angle (neutral position of ailerons) changes in accordance with flight envelope: it does not. Check out this and this Youtube video for an example. Climb, dive, straight and level, no change. The position of the ailerons is not affected by load factor either, as you can see below, 1g (straight & level flight):

... and a pull of 3g's:

(Source: the second Youtube video posted above)
Whenever you see the ailerons move, it is always accompanied by roll.
As for the F-18, I'll investigate and be back later.
(edit: as a preliminary claim I'd say the F-18 drops flaps a few degrees on high g maneuvers to increase camber, but the flaperons only move when roll is comanded or flaps are lowered. So no flaperon up with high g)

But in my video presented here the Mig29 is  in level turn not rolling

@GeorgeGeo ...and in the video the ailerons are in the same position as they are in the picures in my answer aren't they? Just as they are supposed to be.

When a roll is not being commanded, both of the MiG-29 ailerons are in a slight up position.

@GeorgeGeo I found a source explaining the slight upward tilt of the ailerons, I edited my answer to include this information.

On these modern aircraft, there is a thing called flaperons - meaning ailerons and flaps combined, which both move down and up when more lift is needed (TO, LDG and also during some aggressive maneuvers), and are used in order to roll the aircraft.
Also- traditionally- you would assume that the plane uses his tail elevators for pitch, but the contrary is correct- watch rolling F-15 or F-16 and you will see the tail elevators compensating for the wing's inability to roll in various occasions.
I would say that the best and shortest answer would be: Don't try to extrapolate from the basic aerodynamics of a Cessna or a simple aircraft with old school steering surfaces to these jets as they are very different in design and function.
Every plane has it's own very specific characteristic in order to cope with its design problems. For example,  in an F-15 when you roll a full stick aside during a very high angle of attack maneuver, the ailerons don't move in order to maintain stability (otherwise there would be a spin due to aileron drag and other factors).
Try to look at these planes as really fly-by-wire (although some of them achieve the same results of stability using plain mechanical devices and not computers), so elevons, flaperons, and such.
Maybe what you see is actually a momentary roll to the left, resulting in an aileron that is above the profile of the left wing. And another note regarding your question- there is no really such a thing as a "dive" which you can see on the wings. These are very momentary positions of the control surfaces to induce movement and acceleration in some direction. Look at an F-16 taxiing and you will see it's tail dancing in order to compensate for the instability of the G sensor on rough ground.
Regarding your assumption, There are no such loads on such short wings of the combat jets so this is not the reason really. These are just rockets with people strapped to them basically, so they try to be as slick as possible, with just the minimum drag by their control surfaces, using the little lift made by their body and wings with the high speed they fly in.

Stav Nemirovsky The Mig 29 has flaps inboard and ailerons outboard .The F16 uses  flaps and ailerons single command surface called flaperons for rolling but is not the case for MIGs. The elevators differential is used for rolling in this aircraft too , but that is not  the question here .The F15 use rudders at higher AoA for roll s by ARI system

Stav Nemirovsky  ,I  like your thinking about the aircraft complexity but the Mig 29 have only analogue available systems incorporated and some boosted for help pilot with fatigue.

All correct. So show me the movie and i wll explain what he does. Probably- it's just a moentary roll command. And also- i dont really know what goes on inside the mig 29's control computer (such we both understand the F15), but i would guess something there is quite the same. What i can say for sure is that these anes don't  use the ailerons to reduce loads on the wingtips. So next- lets see the movie!

Also- F15 is partially analog, incorporating most of it's mechanism in the analog system.

My  screen recording couldn't be uploaded here.

Can you add a link to a video?

https://m.facebook.com/story.php?story_fbid=548605942390983&id=148530445855064

The video does indeed seem to show the outer and inner control surfaces to be in differing agles, outers more upright than the inner ones.

well, no idea then :)
I will attend my professional help now!
My guess would be some kind of stabilization as maybe the wings in a neutral position give a natural pitch up tendency.

It is possible to be the answer along with the stabilization in rolling

I found the right answer to the question. Maneuver load alleviation device is this function on some jets. These implementations actually schedule symmetric trailing edge (inboard) flaps down while scheduling the ailerons (outboard) trailing edges up. The total lift stays about the same, but more of the lift is generated closer to the fuselage, in an attempt to reduce that total bending moment.

I don't think maneuvering load alleviation is necessary in fighter jets. Even if it was, why is it active in 1G? Anyway as far as MIG-29 goes, the reason for the aileron position is explained in my answer. For F-18 the answer may be different.

At 1 G but high supersonic is necessary to dump some lift ,that's why.

Please provide a source for this answer. While maneuver load alleviation is used on some aircraft, it's not obvious why the MiG-29 and F/A-18, the foci of this question, would need or benefit from it, especially in flight regimes where the loading is low to start with.

“I don't think maneuvering load alleviation is necessary in fighter jets. Even if it was, why is it active in 1G? “I put a new photo of the F15 were the system is active at 1 G

If it's happening at 1G, it isn't "alleviating load".  Redistributing load, maybe. But not alleviating.

True , that is the case. That’s why  I answer my self  to the question after I found the answer .


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Why the Mig21 don't use the ailerons like control surfaces on delta wings at landings or take off?
Mig21 is a delta wing , so why do not use the ailerons like any other delta's ? For lowering the approach and touch down speed. It is not possible that?

Do you mean flaperons?

Yes , the delta use all the  trailing edges for pitching.

I know. But you seem to be conflating pitch authority (elevators / elevons) and high lift devices (flaps / flaperons). Only the latter is used to lower approach speed (unless the elevators have insufficient authority which I doubt on a high performance plane). So which one would you like to know about? Or both?

I want to know if it was possible to use the ailerons like high lift device (camber changed) for lowering the approach speed. There was some wind tunnel trials?

Please edit your question accordingly, then, comments can be deleted at any time. An elevon is not a flaperon so leaving this terminology in is confusing.

Flaperon is something that you use for rolls and pitch, elevons do the same thing.So it is just a different names but functional isn't different.

The Mig-21 is not a delta wing.

. The MiG-21 has a delta wing.

The reason to use ailerons as flaperons on delta wings is twofold:

Delta wings reach maximum lift at a much higher angle of attack, which entails high pitch angle on landing, which is impractical. A way to generate enough lift at a reasonable angle is required.
With low aspect ratio, space on the trailing edge is very limited, so there is a desire to use all of it.

However, there were several considerations against using flaperons on MiG-21:

Overall, MiG-21 is still a 'classic' airplane with conventional mechanical (though boosted) controls. It is not a pure delta which would require special controls by definition.
It is not only classic, but cheap and simple by design. Adding control mixers would complicate the system.
To compensate for the lift problem at landing, two things were used:

Most variants had the 'blown flaps' system, which used compressed air from the engine to blow the boundary layer from above the flaps. The air was injected in the (single) gap of the flap. Like any fighter, MiG-21 had a significant excess of engine power available on landing, and it could be put to use this way.
A somewhat higher landing speed was simply tolerated. The landing speed was about 280 km/h (~150 kt). As one of the results, main tyres were wearing out quicker (I heard the typical lifespan was 5-10 landings).*

(*) That said, the contemporary F-104 was reportedly even worse in this regard, without being delta.

I read that the landing speed is 320 ,340 km/h

No, that's gross. Speeds over 300 km/h happened when that blown flaps system (SPS) was not used, but officially normal landing speed was as low as 250 km/h on some modifications.

I'm no expert on the plane, but wikipedia claims the Mig-21 has separate flaps and ailerons.

On the trailing edge there are ailerons with an area of 1.18 m², and
  flaps with an area of 1.87 m².

The common reasons for not combining flaps and ailerons are that it reduces aileron response and increases the chance of stalling the wing tip (which results in a violent roll in the direction opposite to what you want).
As the Mig-21 has a separate horizontal tail for pitch control, there's no need to use elevons.

So how you could alleviate the  landing speed?

Like the F18 Hornet putting all these control surfaces from the trailing edge in down position.

@George, presumably the designers considered that the flaps were large enough to reduce landing speed on their own. The F18 has to land on carriers, so it needs a lower landing speed. It uses the whole span of the wing for flaps and uses the horizontal tail for roll control.

So the Mig21T  WILL NOT  use the horizontal tail for roll control?I believed that the ALL fighters use differential deflection of the H tail for rolls

Based on the Wiki page (that also says it has elevators) I don't think the Mig-21 uses the tail for roll control, but I'm not an expert on the plane. I think 'tailerons' only became common in later generations of planes.

True the F16 ,F15 use them for roll,at  speed above Mach1, and mig 21 is  Mach2 JET

No, MiG-21 didn't have a differential stabiliser. The next one, MiG-23, had it, but it had no ailerons at all.

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What is the name of the unequal lift distribution across a helicopter rotor blade?
A helicopter rotor blade will generate more lift at the fast-moving tip than at the slow-moving root, unless it is twisted or tapered. Wikipedia calls this "asymmetry of lift", however I cannot find any sources calling it this. In fact, "asymmetry of lift" is used in several sources to mean the same thing as "dissymmetry of lift", which affects helicopters in forward flight.
The sources I've found refer to the use of twist and taper to mitigate the otherwise unequal distribution of lift across a rotor blade, but they don't give it a name. Does it have one?

Wikipedia no longer calls it "asymmetry of lift". "Asymmetry of lift" means the same thing as "dissymmetry of lift", as multiple sources attest.
Wikipedia now calls the phenomenon where the tips generate more lift than the hub "Unequal rotor lift distribution".

To clarify, the question is apparently asking about the distribution of lift along the length of the blade, rather than across its profile.  The question seems to boil down to the following, how to appropriately reference a term for non-uniform thrust loading along the blade, on the one hand, and, on the other hand, that for a design feature to mitigate the consequence of non-uniform thrust loading along the blade. To address the first question, the general term for this unequal lift distribution across a helicopter blade seems to be, non-uniform lift distribution. The alternative, proposed incidentally by the o.p., seems quite acceptable, namely, unequal lift distribution. References reviewed in assessing this issue do not seem at odds with the use of such terms.
The second question is embedded within this context -

The sources I've found refer to the use of twist and taper to mitigate the otherwise unequal distribution of lift across a rotor blade, but they don"t give it a name.  Does it have one?

This part of the question seems to indicate a specific aspect of blade design intended to mitigate the "otherwise unequal distribution of lift across a rotor blade."  This progressive spanwise reduction in angle of attack is literally called washout or twist.  Specifically, the twist is a means of delaying or eliminating tip-stall.  However, twist (as noted in the question) is also used to manage lift.
Saunders (referenced below) mentions this problem -

...if all sections have the same pitch and approximately the same $v_i$ [induced velocity], the tip sections have both high velocity and high angle of attack.  Consequently, the tips produce a disproportionate amount of lift compared to the inboard sections. This is not only aerodynamically inefficient, but creates large moments about the hub with accompanying large coning angles... Designers therefore keep the blade pitch toward the tip about 8 or 10 degrees smaller than that toward the hub, thus altering the angle of attack distribution and obtaining a more uniform lift distribution.

Nevertheless, Wortmann mentions this within the whole context of managing the supersonic field developed along the span of the rotor.  Specifically, design considerations not only regard managing lift along the span of the rotor, but also the onset of, and management of, shockless supersonic flow over the crest of, and along the span of, the rotor blade.
References are many regarding aircraft propeller and helicopter blade and section design considerations.  Here are two that are readily available addressing helicopter blade issues -
Saunders, George H., Dynamics of Helicopter Flight. John Wiley and Sons, Inc. New York. 1975.
Sloof, J. W., Wortmann, F. X., and Duhon, J. M.  The development of transonic airfoils for helicopters. 31st Annual National Forum, American Helicopter Society, 1975.

I think this misses the question. As I read it, the question is about a name for the "asymmetry of lift" generated by a helicopter blade, which is combated by twist, not the name given to the twist in the blade itself or "how to address non-uniform thrust loading along the blade".

@FreeMan, correct. I'm asking for a reference which gives a name to non-uniform load along the blade. Of course, "non-uniform load along the blade" is such a name, albeit a long one without a reference.

Failing that, can someone invent a good name?

"Asymmetry of lift" is a bad name because 1. It is hard to distinguish from "dissymmetry of lift", 2. It has already been used to mean the same thing as "dissymmetry of lift", and 3. The phenomenon has nothing to do with symmetry.

Ok... Ok... I attempted some further clarification...  Sometimes, language is never adequate.

Maybe you could call it a “concave [spanwise] lift distribution”.

Saunders (cited above) has some excellent illustrations regarding the distribution of lift on rotors, and the rotor pitch adjustments necessary for helicopter flight. Just amazing...

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Can induced drag be negative?
For an aircraft in straight and level flight, lift-induced drag is the horizontal component of the force perpendicular to the wing chord. Positively cambered aerofoils generate lift starting at small negative angles of attack. So, could the horizontal component of the force generated by the wing point forward?

I'd say induced drag is the horizontal component of the net force, which may not be perpendicular to the wing chord.

If you explore the concept of the "bell-shaped lift distribution" and how it reduces "adverse yaw", I believe you'll find examples of one wingtip creating thrust rather than drag -- not sure exactly how it works--

After reviewing the answers, I think the flaw in my question is that the total aerodynamic force is not perpendicular to the wing chord.

In KSP if the wings are too small and the tail provides up force, yeah, the blue arrow will point forward instead of up and aft, and then you've designed a plane that does the opposite of right itself.

Can induced drag be negative?

Not for the full configuration, but for parts of it.
Induced drag is part of the reaction force when a stream of air is deflected. This reaction force is split into one component, called lift, orthogonal to the initial flow direction and one parallel, called drag.
Regardless of upward or downward lift, this definition will only result in positive drag. The lowest induced drag possible is zero when zero reaction force is created. Any nonzero reaction force creates positive drag.
For a thought experiment, let's split the deflection into tiny segments, each deflecting the stream a bit more. The initial amount of deflection creates almost no drag. The next bit, however, will already start with a small deflection and add its bit to it. Relative to the initial flow direction, here the flow has already an angle and the reaction force, being orthogonal to the local flow angle, will already have positive drag. The further down we now go, each section will add more drag. The drag component of the reaction force will never be negative.
The only situation where local induced drag is positive is when the local flow hits the lift-creating surface such that bending the flow brings it closer to its initial direction of flow. This is possible on the horizontal tail of a longitudinally very stable conventional design which creates a downforce and flies in the downwash of the wing.

Thanks. In diagrams showing the pressure vectors over the wing, some of the arrows point forwards but most of them point backwards. The total force always points backwards. I think the flaw in my original argument is that the total aerodynamic force is not perpendicular to the wing chord.

@JamesJames If we leave friction out, in separated and fully supersonic flow the total aerodynamic force is indeed perpendicular to the wing chord. Only attached subsonic flow has leading edge thrust which makes the force nearly perpendicular to the direction of movement.

By definition, drag is a force slowing the aircraft down. It is the component of all aerodynamic forces that lies parallel to the flight path of the aircraft. So understood, in thist way, NO, it can never be negative. If it was negative, it would be thrust, not drag.

This misses the point of the question. Let's call this hypothetical force "lift-induced thrust". The question remains, could it exist?

Well, I guess I was not clear enough, or perhaps the logical connection was too large a leap for some. Because drag is defined as the component of ALL aerodynamic forces that lie parallel to the flight path (or relative wind), it cannot be negative. The sum of all forces created by the relative wind MUST lie in the aft, backwards direction! Simply because the velocity if the air pushing vackwards on the front of all aircraft surfaces is higher than the velocity of the relative wind pushing forwards on the back of the aircraft. I would have thought that was obvious.

Unless you want to arbitrarilly define DRAG as some subset of all aerodynamic forces that does not include some of the forces pushing on the front of the airframe.

My question was about lift-induced drag, but you are talking about total drag.

I understand that, but actually, "Lift-Induced" Drag is an artificial abstraction, arising from a simplistic analysis. Lift is not just from the wing. ALL Aerodynamic forces are the Both Lift and drag. The Lift is the part that lies perpendicular to the relative wind, and the Drag part is the part that is parallel to the relative wind. Does it matter that the force on the airframe is coming from the relative wind pushing on the bottom of the fuselage? The F-14 generated a significant component of it's total lift from the cavity between the engine nacelles. Should that be included?

In support of your point, it might be argued (although I've never heard this), that "Induced" drag should be defined as those components of total drag that increase as AOA increases, (hopefully limiting it to those aerodynamic forces generated by the wing, which tilt further aft as AOA increases), but, guess what? that also happens with almost all forces on the airframe.

To rephrase my original question, consider an aerofoil in a wind tunnel, starting at an AOA that generates no lift. The question is: is it possible that a small increase in AOA could increase lift while decreasing drag?

I understand what you're trying to ask. And the answer is No. ALL aerodynamic forces act normal to the local surface of the airfoil. So ANY Increase in AOA will cause the local force vector pushing at each point on the surface of the airfoil to point further aft (The airfoil is tilting aft to increase  AOA). The further aft it points, until it stalls, the larger the component  parallel to the relative wind becomes ...

These last two comments are it.  That’s  all that needs to be said.  Make the “rephrase” 2 up the question, and Charles’s comment just above the answer.  Delete everything else.  Just my opinion, (and not to take away from a few good answers) but there’s a lot of extraneous stuff here that doesn’t really help…

For an aircraft in straight and level flight, lift-induced drag is the
horizontal component of the force perpendicular to the wing chord.

No answer has yet explicitly pointed out, that this definition of "induced drag" is incorrect.  It would be interesting to know where you encountered it.  In horizontal flight, lift-induced drag is the horizontal component of the net force generated by the wing.

I think you have correctly identified the error in my original argument. The total aerodynamic force is not perpendicular to the wing chord.

Not on fixed wing aircraft, but this does happen with rotor wing aircraft and it’s the principal driving mechanism for auto rotation. The section of a rotor blade known as the driven region has an effective force of lift tipped in the direction the rotor spins, driving the rotor blades by means of the air moving through the rotor disc.

Autorotation works pretty much the same way as gliding does in fixed wing aircraft. The induced drag on the blades is aft in direction of relative wind, it's just that the lift itself is tilted forward enough to maintain the autorotation.

… you might potentially say that the induced power is negative (depending on the definition; I am not sure about that), but can't say it about induced drag of the individual blades.

Let's approach this from another direction.
Assume that it's possible to find a wing position that generates thrust rather than drag.  Thrust or drag is a matter of airflow over the surface, to generate thrust we must have a net forward airflow.  Put an indicated air speed sensor in front of the wing, what does it say?  Negative.
Can a plane fly backwards?  No, it would stall.  Thus our initial premise must be wrong--it's impossible to have a net thrust from the airframe overall.  (It is possible to have it for part of the airframe.)

This answer misses the distinction between lift-induced drag and parasitic drag. At an angle-of-attack which generates no lift, there will be parasitic drag. But by increasing the angle-of-attack a tiny bit and generating a tiny amount of lift, could there be a small forward-suction force created? Which would reduce total drag, even though net drag remained backwards? That's the question.

@JamesJames  read about sail boats (they actually use 2 working fluids, air and water, to generate "negative drag").  Some folks around here freak over basic research.  To them, if it doesn't look like an airplane, it's not about aviation.

@RobertDiGiovanni Sailboats are a different case, you have two fluids with very different properties.  Since this is "Aviation" I would assume it's applying to craft entirely in air.

@LorenPechtel  "Two fluids with very different properties" that both produce a forward force.  I think JamesJames is on the right track.  I would recommend studying polars on airfoiltools.com.  At lower angles of attack (before stall), with sufficient Reynolds number and Camber, forward force from the top suction peak produces enough "- drag"  to make net drag much less, yielding some fairly awesome Lift to Drag ratios.

@RobertDiGiovanni, water produces no forward force on a sailboat.  How can it?

@MichaelHall (and Loren Pachtel) it's all about flow over a local surface relative to crafts direction of travel.  An off center fuselage can produce a lifting force, so can a propeller!

Please see sailboat reference.

Thanks @RobertDiGiovanni, when I asked my question I did have in mind Blackbird, a vehicle which can travel upwind and downwind faster than the wind. https://en.wikipedia.org/wiki/Blackbird_(wind-powered_vehicle)

@JamesJames The blackbird works on air vs ground, not pure air.  I'm only talking about a pure air environment.

The understanding of the relationship of drag and thrust in aircraft design is crucial to the development of efficient fuel saving aircraft.
From the aircraft reference, thrust is force towards the line of flight, drag is resistance (from the air) to this path.  Because they are directly linearly opposed, thrust = - drag is mathematically correct, and can be derived from the steady state formula thrust + drag = 0.
Realizing this (simple) relationship can help explain other phenomena, such as "autorotation", extremely low net drag of airfoils, the benefits of slats, and (putting them all together), the design of soaring birds.
All gliders seek to find an updraft greater than their rate of descent.  The broad, highly cambered wing of the eagle is exactly what airliners emulate when preparing to land, allowing them to slow to around 1/3 of their cruising speed.
But what of the slotted wingtips?  Could they be using the updraft to provide thrust?  This seems to work fairly well for auto rotating helicopters, so...
By changing relative wind away from flight path, drag on a part of the aircraft can produce thrust force (negative drag) to the line of flight.  This is accomplished by producing a localized horizontal lift component to the line of flight.
Importantly, to preserve the strict definitions, drag opposes thrust, but localized lift from induced drag can produce a thrust force in the direction of flight.
Now, to get to the point of the question, the Blackbird, and sailing against the wind in general, the key is to extract mechanical energy from a drag force and use it to create a more efficient thrust force in the direction of travel.

Back to thrust = - drag

Let's add in:

thrust = -drag × conversion efficiency

The simplest model would be an anemometer.  Mechanical energy is extracted by the difference in drag coefficient between the closed and open end of a cup.  You could make a Blackbird using a giant anemometer, and it would roll in any direction when there was sufficient wind.

with the wind, faster than the wind

A bit more challenging.  Now we can take the extracted energy and use it to turn a rotating airfoil, a propeller.  Airfoils can generate many times more lift force per unit of drag.
So we turn to iceboats, which can easily sail faster than the wind
by minimizing drag.  Energy input from the wind is amplified by the sail airfoil, creating a thrust force that "runs away" until the total drag (from the entire craft) = thrust (steady state).
The Blackbird propulsion seems to be a form of "autorotation" (with the inner part of the prop blade absorbing drag energy and the outer part lifting).

Oh man-- are you going to get me started thinking about downwind-faster-than-the-wind vehicles again?  Should I block out the next week of my life on my calendar?  Just say no--

Apparently, it's been done.


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Why are holding patterns clockwise by default?
PANS-OPS (Doc 8168), Procedures for Air Navigation Services, volume 2, section 4, chapter 1: "If no operational considerations prevail, right turns holding patterns should be established."
When was this convention established, and why?

Interesting question - especially given the fact that airport patterns use left-hand patterns.

@Pondlife unfortunately not. No references, and the explanation does not make sense: a left hand circuit puts an aircraft on the other side of the runway from the right hand hold, assuming they are landing in the same direction!

The link was interesting though https://www.aopa.org/news-and-media/all-news/2017/may/01/ifr-fix-what-were-they-thinking

I'm happy with the standard explanation of why circuits are to the left: aircraft overtake on the right, just like ships, so the pilot sits on the left, just like cars in countries which drive on the right, so it makes sense for the aircraft circuit to be to the left so the pilot can keep sight of the runway.

I understand that the other question may not have a good answer yet, however this does seem to be exactly the same question. The way StackExchange works is that we try to avoid duplicates. In this situation, the best thing is usually to upvote the existing question, which draws attention to it and gives people more incentive to find a good answer. The [tour] might be useful to explain more about how the site works.

@JamesJames - “a left hand circuit puts an aircraft on the other side of the runway from the right hand hold, assuming they are landing in the same direction!” This is true of a Hold in lieu of a Procedure Turn to reverse course. A right hand turn hold after a Missed Approach would put the aircraft on the same side of the extended center line as a left traffic pattern. This would facilitate a return to the airfield for a circling approach. It would also give the left seat PIC a clear line of sight to the outside of the holding pattern (except when banking).

AOPA also has a few good possible explanations. These include the fact that a right hand hold above the airport separates aircraft from the fixed wing aircraft in a left traffic pattern. Similar to rotary-wing traffic patterns. And, right hand holds near the extended centerline would provide some separation for departing aircraft who would attempt to pass on their right when encountering an approaching aircraft.


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Has anyone built an aircraft with a flat ring wing?
When I try to search for circular wing aircraft, everything I find has the wing loop up over the top of the craft.
What I want to see, however, is basically an Aerobie Flying Ring, but with a motorized propeller, etc.
I'd be equally happy to see a "real" plane, or an RC one.
Also, while I would expect the wing to be attached to the fuselage via cables, I'd be equally interested in learning about alternatives (e.g. blended wing).

George Kitchen patented a design and half-built a biplane. It was completed by Cedric Lee and Tilghman Richards in 1911 but failed to fly. Richards went on to develop a series of increasingly successful Lee-Richards annular monoplanes before the outbreak of WWI.
This was a serious and promising design, having been wind-tunnel tested by the National Physics Laboratory in the UK during development. Kitchen and Richards understood that the strange shape would create vortices which trailed back over the rear part of the wing, and they used these to help impart stability. The monoplanes were indeed all safe and stable in flight (although the first was tail-heavy), a rare characteristic in those days. Pilots included Gordon England, Gordon Bell and NS Percival.

Clearer photos and in-flight videos of a scale model are here.

The closest to a disk I can find is the Vought V-173 also known as the flying pancake

I doubt that, since it wouldn't make much sense.
The aerobie, like frisbie, is spin-stabilized, which is why it is round. But that does not allow controlling it. Controllable aircraft don't spin, so they don't get any advantage from being round.
On the other hand the shape would be very complex, because the profile would have to change depending on the local flow direction. Airfoils that work in both directions are not very good; see Is there an aerofoil that gives reasonably good lift for both air flow directions: forward and backward? That is good enough for aerobie, which at its size has much lower mass for surface area, but wouldn't work for a full-scale aircraft.
And even the complex shape wouldn't be very efficient, because the lift distribution would be far from the optimal elliptic with a lot of lift generated by the sides. The aerobie isn't designed to be efficient at flying at all.
The closest you can have were the experiments with full disk circular wing. Some full-scale prototypes were built, but they didn't show any useful advantage, so all the projects were stopped.


text:
Are there passenger flights with stops in the middle?
Train and bus lines usually have a number of stops along the way where some passengers can get on and off, while the rest stay onboard and continue to their destinatiom. For sufficiently long routes, drivers may be swapped out in the middle of the line, and the bus can be refueled, while passengers stay inside and continue their journey after the stop. But on all the (non-direct) flights I have taken, everyone must get off on the first stop, and get onto a different plane with a different crew to get to their final destination. Why? Are there any commercial flights with at least one stop in the middle, where some but not all passengers get on and off, while everyone else stays on the plane? If yes, why are they so unusual? If no, why do they not exist?

Yes, in some parts of the world, e.g. you have major passenger airports more or less line up, e.g. Beijing-Shanghai-Shenzhen.

Welcome to aviation.SE! This question and this one are closely related, and if you don't get a good answer here you might ask on travel.SE. Some questions that are more travel-related than aviation-related may get better answers there.

Often times, the "direct flight" needed a fuel stop midway, so they would park at the gate to allow passengers to get on/off at the mid-point, increasing revenue and service level. These days, aircraft have massive range, so for long international flights, fuel stops are a rarity, therefore "direct flight" routing is less common.

There also is a slight variation of this for international flights. The same flight might go from, say, Frankfurt to New York and then on to Los Angeles, but you still have to deplane for customs/immigration processing in the USA. British Airways used to have a similar route San Diego-Phoenix-London so they could serve two cities with a single 747 (and take off from San Diego's short runway with little fuel). This was about 10 years ago, this particular route no longer exists.

Unloading the plane becomes difficult.  20% of the plane has to get off, but where in the hold is their checked baggage, now?  Much easier if everyone and everything gets out.  Also, you'd probably want to bring new people on board mid-way so that the plane isn't part-empty.  Unless you unpack and re-pack the luggage at each stop, that gets a bit tedious.  Or you fill it with cargo and those flights now would have no baggage allowed ever.  Also a tough sell...

Virtually every Southwest Airlines flight.

I would like to add that there are also technical stops for refueling/inspections etc. Once had a technical stop due to very strong headwind so needed to refuel to in order to reach destination.

20 years ago I flew from Canada to Prague and back with CSA which flew a "double hop" flight: Prague - Montreal - Toronto - Prague.  People going from Montreal to Prague had to flight an hour in the wrong direction, wait for the stop and fly back.  I imagine they weren't thrilled about this, but the level of traffic didn't make two non-stop flights economically feasible for CSA.  I think these days it would be more likely that they would do a code share with a Canadian airline in a more hub + spoke model.

This always reminds me of the great opening "map" sequence in Indian Jones !

Example from my 2009 Jordanian airlines flight: Boarded at Hong-Kong. Landed in Bangkok, 80% of the passengers left, I remained at my seat as ground crew cleaned-up the plane, and then different 80% passengers came in. Takeoff, and then land in Abu-Dhabi (though it wasn't on my itinerary) to fuel-up, and one guy got off. Then finally landed in Amman.

These "direct" flights are actually not unusual, at least in the US. I was surprised by this discovery based on the routes I personally tend to fly, but fortunately we have the Bureau of Transportation Statistics to provide objective information. Using the July 2019 data for all major carriers, I identified direct flights by counting multiples of the same flight number on the same day with the same aircraft, as opposed to single-segment "nonstop" flights. Here's what I found:

Some interesting notes:

Over a third of all flights are direct.
The practice is not limited to low-cost carriers. In fact, the two largest traditional carriers (American and Delta) operate around half of their flights direct and together operate almost two-thirds of all direct flights.
Nevertheless, Southwest uses more direct flights for its size than any other airline, nearly rounding out the other third.
On the other hand, JetBlue, which is commonly considered a low-cost carrier, barely operates any direct flights. Other low-cost carriers use anything from zero (Allegiant) to about a quarter (Spirit, Frontier) direct flights.
The other traditional carriers use direct flights sparingly. Hawaiian flies only nonstop routes, which makes sense.

I may have missed a few direct segments that departed past 12am on the day after the previous segment, but I don't think there's enough of those to substantially alter the results. In any case it would just increase the number of direct legs.
It'd be interesting to run some more analyses to see historical/annual trends in the practice, but that would require someone with more patience and/or computing power than I have. These data sets are huge and can only be downloaded month by month. I chose July 2019 because that was about the peak of commercial passenger aviation.
There's also some fun aviation memorabilia associated with these "direct" flights:
(source)
On airlines with no assigned seats, plastic cards like this used to be provided so that even the passengers continuing on could deplane if time permitted. Somewhere I have a couple old ones from Alaska Airlines. Nowadays I believe the airsickness bag doubles for this purpose in some cases. I suppose if you really didn't want someone to take your seat, you could leave a full one behind.
Note: A previous version of this answer had a much lower count of direct flights. Turns out Excel just wasn't done calculating yet.

I’ve been on several legs of AA “direct” flights. They go spoke-hub-spoke or hub-spoke-hub with approx. zero through pax. I’ve never seen a hub-spoke-spoke or spoke-hub-hub flight.

I did "Barrow-Fairbanks-Anchorage" with AS a few times back in the day - you just stayed in the plane and that was it.

Note that "same flight number" does not always translate into "same equipment". @htmlcoderexe Similar experience here. I flew from Anchorage to LAX. That was a continuation of a flight from Fairbanks.

@KevinKeane I only counted continuations with the same airplane.

I definitely have been on a three-stop trip from PHL to SFO where my wife and I stayed in our seats while most of the rest of the passengers got off, and then the next passengers got on. Since none of the legs were long enough to (individually) justify dining service, we ended up eating a lot of peanuts. I’m pretty sure our stops were in Kansas and... Colorado?

@StephenS: I'd be very surprised if a significant number of spoke-spoke segments exist in the first place. Spoke-spoke defeats the purpose of the hub-and-spoke model, and depending on the spokes, you might run into insufficient demand. As for hub-hub, in general my expectation for such segments is that they are huge long-haul flights with twin-aisle planes. You're (probably, in most cases) not flying one of those planes to a spoke.

@Kevin Exactly my point. They do have a few spoke-spoke flights where demand warrants, but I’ve never seen them direct, only nonstop.

@StephenS: Note, I was talking about segments, not flights.

+1 for “leave a full one behind”

@StephenS: not being American, I am not sure where the flight Phoenix-Portland-Oakland I took once by mistake (wanting to fly from Phoenix to Oakland) falls in your list (Phoenix seems large, so "hub", Portland I do not know, then Oakland seems to be a spoke - that would make hub-spoke-spoke or hub-hub-spoke)

I'd second the point @StephenS makes about AA. At a small airport near me (FSM) we have an AAL3180 flight that operates each that from DFW-FSM and then FSM-DFW. That'd be a "direct" flight by the definition in this answer but I guarantee almost no one is riding through ;) Depending on how much AA uses this arrangement, most of their "direct" flights might not really be what we're expecting.

@JeffB makes a good point.  On the route I'm personally most familiar with (Atlanta-Philadelphia), I've seen Delta use a single flight number on ATL-PHL-ATL (Atlanta being a Delta hub) and I think I've seen American use a single flight number for PHL-ATL-PHL (Philadelphia, like DFW, being an American hub).

These are known as “direct” flights. They aren’t popular because each stop adds an hour or more to the travel time for through passengers, so they are significantly slower than non-stop flights yet little better than a connection.
This actually used to be the norm, but in the last few decades most larger airlines have moved to a “hub and spoke” model with plenty of connections at the hubs. They may have some spoke-hub-spoke or hub-spoke-hub direct flights on the books, but in practice virtually all of the passengers change at the midpoint. It is quite rare to see hub-spoke-spoke or hub-hub-spoke direct flights.
Some hub-less low-cost carriers still feature direct flights.

You can still sometimes get a direct flight, if your origin and destination are both spokes off the same hub.

@Mark Possible, but with a dozen or more spokes off each hub, the odds of a direct flight on your particular spoke pair are tiny.

I think another reason is also simply because aircraft have gotten larger and larger ranges, where a non-stop flight is more fuel-efficient than one with a stop.
In the '60s, Shannon airport in the west of Ireland was one of the bussiest in Europe, just like Gander (eastern Canada) was for Northern America.A lot of passengers wanted to go from Europe to the US had stopovers over there, while nowadays it's a lot cheaper to go non-stop.

I remember flights like this in the 80s and early 90s, and the time wasted at each stop was definitely annoying.  It was also extremely awkward, with the crew trying to quickly clean a cabin that was still half-full. The only real advantage over a connection was you're less likely to lose your luggage since it doesn't have to change planes.

Yes, such arrangements are not uncommon in routes served by commuter airlines and smaller regional carriers. At a stop, the "through" passengers remain seated while others deplane and new passengers enter.

Sometimes you have to disembark and reembark

@antzi, yes, and sometimes not.

KLM still flies their AMS-DMM-MCT route as a direct flight. Not exactly a small regional carrier. I'm sure there are other examples too.

Another example is UIO to SCY on TAME - this makes a stop in GYE. Passengers transiting via UIO do not have to disembark in GYE while waiting for GYE passengers to board or deplane. (as of May of this year TAME doesn't exist anymore but I believe LATAM offers the exact same flight). I am pretty sure that the reason this is done is because environmental regulations only allow a certain amount of flights to come into the Galapagos so the airlines stuff both of their originating destinations on the same plane

@Sanchises Amsterdam-Tenerife operated by KLM used to be one (don't know if it still operates, last time I was on that one was 6 years ago). About 45 minutes stopover in Madrid. No refueling or passengers on/off, but crew change and mail-bags on/off.

As others have pointed out, “direct“ flights do exist. The airline will have the same plane travel from one city to another with a stop or two along the way. On those flights some passengers will disembark at the stop as that is their destination. Other passengers will get on at the stop to go on to the other destination.
Flying out of Love Field, this arrangement was the norm with Southwest Airlines. This was due in part to the Wright Amendment.  Since, I now mostly fly American Airlines out of Dallas Fort Worth Airport, I do not know for certain how much the repeal of the Wright Amendment has changed this. But, I do know that it is still relatively common.
The longest flight that I personally know of that did this used to be South Africa (probably Jo-burg) to Texas (Dallas or Houston) via Morocco. To my knowledge, this route no longer exists.

WN, as of the last time I flew them (a couple years ago), still does "hopscotching" routing with their aircraft, with direct multi-stops being common.

In 2007-2010 there was a Johannesburg - Dakar, Senegal - US East Coast flight as well.  I don't recall the US airport but I think it was either New York JFK or Washington Dulles.  A friend of mine flew this flight to get from Johannesburg to Philadelphia.  It looks like they've also run a Johannesburg - Accra - Washington  flight as  well.

That's just because of your city-pairs.
What you're really saying is "Everytime I fly, I must go to an intermediate "hub" airport and change planes".  That's not true for everyone, it's just (all due respect) true for you, because of the airlines and city-pairs that you do fly.
It's actually perfectly common for an airline to have a "numbered flight"  that flies from city A to city D to city M to city Q to city W. It's the same aircraft, with the same flight number, and sometimes is serviced or changes crews enroute, rather like a train or bus actually.
The crew changes aren't necessarily due to exhaustion; often they're to return the crew to "home base" at the end of the day, so they can go back to their families, without the airline having to pay for hotel, transport, per diem etc.
For instance, pre-COVID, a US airline (Southwest) flew a whole bunch of cities.  And they tended to scramble up which flights flew which routes, so that most city pairs had a straight-through flight if you waited long enough.  Let's take a hypothetical airline,  and wanted to get from city A to R... here is a day worth of eastbound flights, each typically 3-4 hops:
 114: A - E - N - Q - X
 121: A - G - M - T - Y
 128: B - E - R - W
 131: B - F - M - S - X
 133: C - G - M - R - Z
 189: A - H - L - R - W

So for instance, I could fly Flight 114 then change planes at E to flight 128. So that's exactly like your experience; you have to change planes somewhere.
Or I could fly Flight 131 and change at M to Flight 133. In this case, I'd go through F, but I'd stay on the plane. So no gathering bags and piling off the plane etc.   I'd still have to change planes at M. That's where Spirit differed from Southwest; Spirit would kick you off at F, even though you'd get right back on the same plane.  All of them may do that today due to COVID cleaning.
Or if I waited until later in the day, I could fly flight 189 and not have to change seats, though we would still stop 2 places.
Notice how none of the flights from A and B go to the same destinations twice. That's an example of the airline "scrambling it up" so most city-pairs have at least one flight a day with no plane changes, specifically to serve customers like you who dislike them enough to settle for that flight time.

why are they so unusual?

You could turn the question around and ask why bus and train companies run sectors where the vehicle is mostly empty and making a loss. Often it's because the city requires a minimum level of service for remote areas as part of the franchise.
Also, it's cheap and easy for a bus or train to stop and change passengers, but an airline might find it more efficient to use a smaller plane for the 'spoke' flights and a big one for the hub-to-hub flights.

It's also common in areas with islands. Many flights into Cape Verde islands hop one or more islands along the way in or out. Apparently it's lucrative enough to hit the airports in the region instead of having seperate flights.

Sure. Flew Amsterdam-Dubai-Jakarta a few years ago that was just that, just the people needing to get off in Dubai did so.
Same with a flight a long time ago Amsterdam-Bonaire-Curacao.
Fuel stop in combination with letting some passengers on and off.

I flew Amsterdam - Doha - Muscat. The passengers bound for Muscat stayed on the plane in Doha while the passengers for Doha deboarded and a few boarded for the leg to Muscat.

@Alexander were these both Emirates (yours and the answer)? I had similar in 2015, EK418 Bangkok to Christrchurch with a stopover in Sydney, and then EK419 was booked as Christchurch to Dubai (with stops in Sydney and Bangkok).

@llama mine were KLM and Garuda.

@llama Mine was KLM as well, which is why I commented on this answer.

Southwest Airlines in the US does it all the time.  Here's a flight from Houston, TX to New York, NY that has a stop in Atlanta, but still only a 5 hr flight end to end.
Note the "1 STOP - no plane change" here on the flight listing on their website:

And checking on the actual flight tracking shows the stop in Atlanta, but both legs are the same flight number.  From my experience, ~1/2 the passengers will stay on the plane.

MIAT used to regularly fly from Berlin to Ulaanbaatar with a stop in Moscow. All of the passengers had to get off (and on again) in Moscow, although the plane and quite probably the crew would stay the same.

Most of the answers focus on the US, but there are lots of such flights on international routes, at the very least on the Europe-Australia flights operated by European or Australian airlines, most of which have a stop somewhere in South-East Asia (Singapore, Bangkok...).
Those flights are long enough that all passengers actually deplane before re-boarding (and they do a quick clean-up in the meantime), but IIRC you can leave your stuff on board. Of course, all crew will change at the intermediate stop.
This is becoming less common as many airlines have a tendency to do partnerships with one airline flying each leg with its own aircraft.
If you go back a few decades (before long-haul aircraft), it was very very common. The same "flight" (using the same number and aircraft) was actually a succession of many shorter hops up to the maximum range of the aircraft. The Kangaroo route used to take well over a dozen stops.

Widerøe definitely do this in the north of Norway. You can read about one traveller's experience of the Tromsø-Hasvik-Hammerfest-Honningsvåg-Mehamn-Vadsø-Kirkenes "milk run" here:
https://simpleflying.com/flight-review-wideroes-explore-norway-pass-land-of-the-midnight-sun/
Here in Finland, I know that (pre-Covid, anyway) one of the Helsinki-Kemi flights had a short stop in Kokkola.

This is basically a milk run flight. I'm aware of two: Alaska Airlines runs one in Southeast Alaska from Seattle to Anchorage, and United runs one in the Pacific, from Honolulu to Guam. I've been on the Southeast Alaska one—if you're a through passenger, you don't really have time to get off the plane and use the airport facilities.
https://simpleflying.com/milk-run-flight/

There are various intercontinental, some as extra stop, and some as "triangle flights".
E.g. Air Canada going from Canada, to Argentina and then Chile and then to Canada (or the contrary). If you need to go to Chile, you have a stop in Argentina, where there is change of people. But if you stopped in Argentina, at flight back, you will stop in Chile.
There is also KLM (really "KLM Asia"), from Amsterdam to Taipei and then to Manila. And then back: Manila, Taipei, Amsterdam. So you have a stop to get new passengers (and fuel).
In US some years ago I booked a direct flight from Seattle to Boston, and I was very surprised that such flight stopped in Denver (and just few passengers stay in, for the full journey). [By the way, it had also an unexpected technical stop in Hartford, because of lack of sufficient fuel, because of unexpected traffic at destination]

This also used to be called "continuing service". Like "flight 123 to ABC with continuing service to XYZ". But then the airlines started getting creative and using the same flight number but not the same plane or crew so they could market it as one flight and show up higher in search results.
One other reason why this is less common (besides spoke-and-hub in general) is that airlines have gotten much more deliberate about filling every seat. So in the above link, the first leg uses a slightly larger plane than the second leg. Probably the smaller plane is too small for the first leg, but the second leg doesn't have enough traffic to justify a larger plane.
I have seen this when there were two airports really close to each other (flight A to B to C where B to C is very short). My guess was that people from A were willing to pay enough extra to get to the exact airport that they wanted that it was worthwhile, but no one would actually pay to go from B to C if they weren't already on the plane so it wasn't worth keeping a second plane there. Or maybe some VIP lived there and really wanted it--crazier things have happened.


text:
Which type of airfoil does the 737 use?
NACA airfoils are not used anymore except on some aircraft. So which type of airfoil does the 737 use? Which company designs it and builds it?

I think Boeing still designs the airfoil.

Boeing designs and builds them. Why would a large aircraft company not design and build something so fundamental to its planes?

Boeing designs its own airfoils for its aricraft. According to this site, the following airfoils are used in 737:
Boeing 737-100: Wing root- BAC 449/450/451; Wing tip- BAC 442
Boeing 737-200: Wing root- BAC 449/450/451; Wing tip- BAC 442
Boeing 737-300: Wing root- BAC 449/450/451; Wing tip- BAC 442 mod
Boeing 737-400: Wing root- BAC 449/450/451; Wing tip- BAC 442 mod
Boeing 737-500: Wing root- BAC 449/450/451; Wing tip- BAC 442 mod
The 737 wings are manufactured at the Boeing plant in Renton, Washington.

How about the tails? Horizontal and vertical.

Tail sections usually use symmetrical profiles such as the NACA0009 and (slightly thicker) NACA0012. Although the exact airfoil is not specified, this answer confirms those thickness ratios for the Boeing 737-100 as well.

From this site, contains links to the profiles which can be used for Xfoil.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What is a Pressurization Safety Valve?
Here you can see two of them on the B747. What are they and what's their function?

Source: FAA's Pilot's Handbook of Aeronautical knowledge

The pressurization relief valves are on the left side of the fuselage and are used to provide protection (for the aircraft) against excessive differential pressures. In this case, they are set to open at a differential pressure of 63.8 KPa (with 66.9 KPa) as a backup. From ATSB Investigation Report on the depressurization of Boeing 747 VH-OJK:

The relief valves provided protection to the aircraft against excessive differential pressures, with the external latching doors providing a positive indication of valve operation. Aircraft systems documentation
  specified that the valves open at a differential pressure of 63.8 kPa (9.25 psi) to vent the fuselage interior to the ambient atmosphere. An additional relief setting of 66.9 kPa (9.7 psi) acts as a backup.

The same report shows the external blowout doors of the (both) relief valves open, as shown below.

In a related note, there is a negative pressure relief valve to prevent vacuum damage to aircraft during a rapid descent. Usually, this is a spring loaded valve that opens inwards at negative pressure differential.

The purpose of pressurization safety valves is to prevent too large differential pressure in the pressure-hull.
The safety valve(s) are normally closed, and they're set to open in a certain differential pressure. So for example in case the normal outflow valve fails for some reason and is closed, and the ac-packs continue to push pressure in the cabin, the safety valve opens thus maintaining a safe differential pressure.
They are a part of the pressure hull "safety back-ups" just like the negative pressure relief valve too.

Yes, and the purpose of preventing too-large pressure differential is to avoid structural damage. As an added note, the valves in the 747 pictured in the question open at a differential pressure of 63.8 kPa (9.25 psi), with an additional backup relief at 66.9 kPa (9.7 psi).

And... The photo in the question technically shows the blowout doors downstream of the valves. The doors latch open after any over-pressurization event.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What holds the overhead lockers?
If they carry a lot of weight inside, what avoids them from falling down to the passenger's heads? What holds them? How are they mounted inside the cabin?

Screws into structural frames

Are you asking about the design structure of how the overhead lockers are mounted in the aircraft? Or are you asking about the latching mechanism for the overhead lockers?

@JonathanWalters I'm asking  about how they are mounted in the aircraft

The overhead bins are usually mounted to the aircraft structure. For example, in case of Boeing 737, they are mounted to the stingers using tie rods. From an accident report of Boeing 737-400:

The forward inertial load is reacted by a diagonal tie, mounted at one end to stringer 6 or 7 in the fuselage crown and at the other end to a fitting on the upper surface of the bin. The vertical and lateral loads are reacted by short tie rods attached to the fuselage.

B737-400 overhead bin attachment. Image from the same report.

authors: Артемий Волынский

authors: العوام عبدالله الشيباني


text:
What happens if you exceed the maximum speed on a C172?
The airspeed indicator has a red marking that means: "never exceed this speed" ($V_{NE}$, around 160 KIAS). Why can't you exceed that speed?

You can, but you have to live with the consequences. There are several things that can happen:

Depending on the vertical gusts ahead, you might not even get close to v$_{NE}$. There is another speed limit for gusty weather called v$_B$, and exceeding this will run the risk of overstressing the wing structure. Going above v$_B$ will overstress the wings in a gust of more than 50 ft/s, and more than 25 ft/s when flying above v$_D$. The exact values can be found in the flight envelope diagram of the flight manual.
On a calm day, you can fly v$_{NE}$ and even a little faster, but once you fly fast enough, flutter will become very likely. Note that flutter needs some initial excitation, so you might fly well into the flutter speed range before flutter occurs. When it does, control surfaces will be ripped from their fittings which will make the aircraft pitch up. At that point the wings will break off.
The engine on a C 172 is not powerful enough to sustain level flight at v$_{NE}$. You need to dive the aircraft, which requires some altitude. Maintaining the speed will mean that you dive into the ground, so you need to pull out of the dive in time.
On really fast aircraft the pitch trim will get more nose-heavy when the aircraft approaches the speed of sound. You don't run that risk in a C 172, but faster aircraft found themselves locked into a dive which they could not end.

Note that for the C172, the published Vtap is probably more relevant than Vb (which I don't believe is published in the AFM).

Or as it may be, not live with the consequences :-)

At that point the wings will break off. I hear from time to time about things that can make the wings break off, but then to the contrary I hear a lot about how the wings can't come off under anything but the most extreme circumstances, and stress tests where they show the wings buckled at a very large angle before something fails..

@Michael: Fly fast enough and everything will come off. Dynamic pressure is the thing to watch here: If it is high enough, even small angle changes will unleash immense forces.

A few questions on Vne:  1) is the primary risk in exceeding it the onset of flutter at the natural frequency of the structure leading to structural failure?  2) Or are the drag loads on the airframe reaching the point that certain primary structures are approaching the yield stresses of the material?

@CarloFelicione Not drag, but lift. It is higher by L/D, after all. For certification you need to prove a flutter margin of 1.2, which is 1.44 in dynamic pressure and lift.

You can exceed the never exceed speed $V_{NE}$, but doing so will most likely result in damage to the structure. From FAA handbook of pilot knowledge:

$V_{NE}$ —the speed which should never be exceeded. If flight is attempted above this speed, structural damage or structural failure may result.

Speaking of the FAA — if you exceed V_NE, then your airworthiness certification becomes void.

@200_success This is only a concern if you live through the experience.

@MichaelHampton Presumably there is some safety margin built into the limit.

Because above that airspeed, the airframe is increasingly likely to fail.
Failure would likely start with control surfaces like the ailerons, elevator and flaps, then the wings and tail are likely to separate, resulting in total catastrophic failure.

Think of $V_{NE}$ as the speed at or beyond which the structural integrity of the airframe is not guaranteed.
In other words, parts of the airframe - which is critical for controlled flight cannot be guaranteed to perform as designed.

There are both aerodynamic and structural reasons for Vne.  Aircraft controllability is impacted (for specific impacts on a specific make and model, consult with the manufacturer and perhaps they will share their findings from testing) and you may encounter difficulties with control authority (your ability to move control surfaces), airflow (e.g. the Clark-Y airfoil is designed for its lifting capability far more than it is designed for speed), and you may exceed the structural limits of aircraft components (control surfaces, wing spars, windshield, landing gear.)  Operating above Vne now places you in the role of de-facto test pilot and any damage you cause to your aircraft may manifest itself that same flight or many hours later when the results of stresses you induced on the airframe or cables, pulleys etc. cause a failure of the aircraft structure.

The answer depends on how much you exceed V_ne.  I do not have the information for this particular aircraft in front of me, so I can not say what will happen at a specific airspeed.  Cessna spent a lot of money and time on engineering and flight testing to come up with the maximum airspeed (V_ne).  There is a safety factor built in to this calculated and tested speed.
One situation is flying level at a high altitude, then go in to a steep dive.  This may cause an overspeed condition.  One of the first problems as a result of overspeed, will start out as a vibration of control surfaces and controls. The chance for loss of control by the pilot due to mechanical failure or metal fatigue will increase exponentially, as does the airspeed.
The C172 has airfoil designs meant for low speed. Depending on the exact plane and loading this could differ slightly, but the stall speed is 49 KIAS.
With its straight, high lift wing structure,  the airfoil may actually completely loose its lift at a very high airspeed.
As the airspeed increases, farther above the V_ne, the craft will basically start to tear apart and disintegrate.

As stated in another response the stock engine in a C172 isn't powerful enough to sustain Vne in horizontal flight.  Establishment of the various speeds is part of the aircraft certification process and usually includes a safety margin of 10 to 15 percent and there are many factors that go into determining these numbers.  For example, I have a Beachcraft Baron and one of the important speeds is Vr or V Rotate.  It's not that the aircraft cannot take off at a slower speed it's just that if you have a critical engine failure at takeoff power and a slower speed you don't have enough control authority to compensate.  There are many factors that go into determining these numbers and structural integrity is just one of them.

This doesn't directly answer the question and is better off as a comment.

To add to previous answers, Vne is usually set at near ideal conditions, therefore the 10% - 15% mentioned above really becomes nothing if there are air pockets or other phenomena usually not meaningful, let alone minor fatigue or skin imperfections, hence, as the name implies, never exceed this speed with standard issue airplanes.


text:
Do airlines ever clean their planes?
Looking at some photos, I saw that a lot of planes are very dirty (on the fuselage, not inside or in the cabin), and it is said that the dirt on the fuselage affect performance. Also insects affect the aerodynamics of the plane, so, do airlines ever clean their planes?

they do usually during scheduled checks when the plain is on the ground for an extended period anyway. They also repaint them periodically.

Yes

Several incident were result of improper cleaning procedure, including Aeroperú 603 and XL Airways Germany 888T

@Him, you mean accidents, don't you?

In addition to repaints, aircraft are also periodically washed and treated to maintain the paint quality and reduce the build up of dust/grime/salt and other particulates.
There are automated systems installed at some airports to clean airplanes as they taxi over these areas. Think of it as a drive through car wash, but for airplanes.
The very first applications of these were actually for the US Navy because they have a requirement to wash aircraft due to their proximity to seawater. A company called tammermatic developed a system for the navy to clean airplanes directly on the field using a set of powerful jets. Images from the tammermatic website

Then there is the Skywash system (PDF brochure), developed by PMW (a company that makes concrete pumps) to wash aircraft automatically. It was first used by Lufthansa in 1997 (image cc: ARNE DEDERT / AFP):

Side note: the Skywash brochure uses "aircrafts" instead of "aircraft". English is hard...

@FreeMan That’s a Britishism, like 'maths', or 'drugs test'. Since they are a German company, they are probably more familiar with British English.

@JScarry "Aircrafts" Is not a Britishism that I have ever heard used in Britain (except by people speaking EFL).

@alephzero It seems to be a popular way of writing the plural form at the BBC. https://duckduckgo.com/?q=bbc+aircrafts+-aircraft&atb=v69-4&ia=web


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What is this line found above the door on many aircraft?
Many aircraft have this line above the door as seen in the photos below. What is it, and what is its purpose?
Source

Source

These are rain gutters.
They are designed to catch rain that runs off the upper surface of the aircraft fuselage and channel it away from the open aircraft door so that the water does not enter the cabin.
This is a close up of the rain gutter over the main cabin door of a Beechcraft King Air B200, showing the channel that would catch and redirect water flow to the side of the door opening:

Source: own work
A jet-bridge may partially deflect rainwater in some cases, but the gutter helps mitigate water exposure for the aircraft interior and passengers. Even gutters cannot completely eliminate such exposure since their size is necessarily limited by aerodynamic constraints. Many operations do not have the luxury of jet-bridges, making the rain gutter especially helpful in reducing the amount of water that might otherwise enter the cabin and pose a hazard to the aircraft or onboard systems.
"Rain Gutters" is the technical name, at least for Boeing aircraft, such as the B777 depicted in the photos in the question.
Here is a Boeing reference to such gutters on the 787:

Rain gutter: When customers found that water was not being properly deflected
  over a passenger entry door, they requested a change. Boeing relocated the
  gutter to function more efficiently. The solution means happy customers, who had
  fewer water and maintenance issues, and happier and drier passengers. This
  was a significant enough change to process to require certification work with the FAA.

This was a significant enough change to process to require certification work with the FAA. You know I'm not usually one to gripe about onerous regulatory requirements, but sometimes you just have to facepalm.

Yeah, I thought that was noteworthy. I suppose there might have been legitimate reasons if moving or reorienting the gutter affected structure somehow. I don't know how Part 25 certification processes go.

"Rain gutter" is also the name for the analogous structure on your house that stops water falling off the root onto you.

I like it how the description focuses on the large amount of happiness produced

I assume their alignment approximates that of the airflow during cruise.

@sdenham Yes, I have read that the gutters are oriented to align to some degree with local airflow, though I imagine a tilt off of ground horizontal for water flow is also a design consideration.

+1. These are also used on land transport vehicles, buses especially, for the same reason.

It's for the passengers on a rainy day. If this strip would not be diverting the rainwater flowing from the upper fuselage, a curtain of water would soak the passengers upon entering or leaving the aircraft, and the cabin floor.

These rain gutters are for deflecting the rain from entering the cabin. Even with Jet-bridges, the door itself might be covered, but since the whole cylindrical fuselage is not. The rain that falls in the uncovered area at the top of the fuselage would roll down, then going under the jet bridge's cover. This is to redirect that water that would have gone into the doorway off to the side.

This doesn't add anything to the existing answers.

It's used so when they are attaching the air bridge, it helps the top of it to align.

Welcome to aviation.SE! Can you quote any source for your answer? It seems to contradict what other answers have said.

To anyone who sees this answer in the automated review queue, please consider downvoting rather than deleting answers that you believe are incorrect but on-topic.


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What is the Effect of Unsynchronized Propellers?
A long time ago, I had the privilege of flying in 4 engine turboprop airplanes in which the props were 'synched'(blades rotating in same speed) which of course is necessary for smooth thrust.
However, one of the exercises we performed(as a military aircraft) was called a "crash and dash"; we dove as steep as we could until we could get as close as we could to the surface, then pull out of the dive and attempt to 'fly below' any surface radar that may be tracking us.
Every time we did this maneuver it threw the props out of 'synch' and cause the airframe to shudder violently. Anything that was literally not 'nailed down' was thrown through the cockpit or cabin.
My question is, what effect does this have on the airframe and does one of the events require an inspection, or shorten the check cycle?

It sounds like it may have been the high g-forces which caused the violent shudders and not the props being out of sync (which normally wouldn't cause those kinds of forces).

@Lnafziger I can't say for sure how many G's-I wasn't 'pinned' in my seat and we didn't need G suits. But it definitely threw the props out of synch whenever we attempted it, and the result was a violent 'juddering' (I suppose caused by the acceleration of force against props that were increasingly unable to hold synchronization....?

It is called hunting and well explained in this answer. It seems that the frequency difference was equal to a structural eigenmode. Looks like shoddy piloting to me. The effect on the airframe: Do it long enough and it will fall apart.

I think it's more likely that the wings started fluttering than that the props shook the aircraft.

@PeterKämpf Thank you for that reference-I tried my initial search and I didn't come up with it. The wings of a Lockheed Orion are pretty stiff, and I have seen landings in 45mph crosswinds in them(Adak or Shemya). It is definitely the prop synch that was exacerbated by the steep rate of descent-something hopefully you will never have to do unless you are evading a SAM lock-on, or landing at a 'hot' airstrip.

Another possibility is buffeting: In a dive the airplane might pick up enough speed for supersonic flow over the wings. This ends in a shock, which can oscillate and cause the vibrations you describe. The propellers-out-of-sync explanation (while possible) is less likely. The Orion gained a reputation in its brief civilian career of throwing whole wings off due to resonance with a damaged engine mount. I expect that Lockheed did make sure in later versions that vibrations coming from the engines would not cause resonance somewhere else in the airframe.

I would agree with the other comments, in that I don't think the extreme buffeting could be caused by out-of-sync props. Maybe if you lost a chunk of a blade and you had out-of-balance props, but that's a bit different. Or if one of the props came WAY out-of-sync. But I know nothing of the Orion aerodynamics or engineering.
My twin experience has been more of the light piston and turboprop variety, but I can tell you that out-of-sync props produce a "whah whah whah" sound that will drive you absolutely bonkers. As soon as I was straight and level, I'd match rpms/prop pitch on my engines (or turn on the prop sync) to get rid of the noise. I never wanted to try it long enough, but apparently acoustic oscillation like that can cause serious fatigue. And I would imagine that long-term exposure can't be good for the airframe.


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Why are there no blended-wing passenger airplanes in operation?
Blended wings are more beneficial when it comes to fuel efficiency increase and noise reduction. However, no manufacturer has decided to produce these airplanes for major airline operation so far. What are the inhibiting factors in the industry for not using this configuration?
From what I can guess:

It is a complete new configuration with low experience on it. High risk.
Aircraft will be in VLA sector (>500 passengers), a sector not very attractive nowadays.
The 90 seconds evacuation limit needs to be observed.

Related: Why is there really only one basic design for passenger airplanes?

also window seats, self loading cargo likes seeing the outside. and a good window is vertical

From the related question I have also extracted extra weight due to pressurization shape (eliptical vs rounded) and adding on top of risk the certification risks (but that's somehow similar to composites introduction).

@TrebiaProject There's a lot more risk trying to get an entirely new design certified for passenger service than trying to get the same design with different materials - in the latter case, it's a question about material properties, while in the former you have a totally different structure that is already known to have possible regulatory issues (e.g. evacuation), and has to take a lot more stress from pressurization.

@cpast agree, you have a point.

Here's a related question:  http://aviation.stackexchange.com/questions/8649/why-is-there-really-only-one-basic-design-for-passenger-airplanes

Same link as before.

All studies which so far showed an advantage for blended-wing bodies (BWB) were flawed. They get published because of that "publish or perish" circus performed in academia and PR.
The trick mostly used is to compare an existing airliner with a hypothetical BWB which uses equally hypothetical engines of improved efficiency, like what could be expected 20 years into the future. This masks the inefficiency of the BWB concept and makes the combination come out ahead.
The BWB will always have more surface area than a comparable conventional design. Why?

Being tailless, it cannot compensate for the pitch change resulting from flap deployment. Consequently, the wing area must be much larger than in a conventional design to enable tolerable field lengths.
The flat fuselage shape needs a less efficient pressurized cabin of oval or double-bubble cross-section. This drives up empty weight.

The larger area translates into more friction drag and more skin mass, which more than offsets any advantage given by the bigger wing root (which helps to reduce wing spar mass). If you like real data, use the Avro Vulcan as an early BWB and compare it to its contemporaries. Note that design attempts for an airliner based on the Vulcan (type 722 Atlantic) went nowhere.
The larger wing area offers another method for deception: Referenced to that large area, the drag coefficient might look smaller that that of a conventional design, but once we compare real drag forces, the conventional design wins hands down.
Why are these BWB studies published? The authors gets more attention when they claim a "revolutionary breakthrough" than when they are more honest and admit that the concept is a dud. Even Boeing or Airbus like to publish BWB studies, so the public gets the impression they are ahead of the competition. It is sickening to read such academically dishonest studies - you need to spend time to dig to the bottom of the thing and to unravel the plot; however, once you have done this a few times, they all become alike. But compared to studies made 60 or 80 years ago, where the author factually lists what he did and why it didn't work out (which is the only way you can learn something), those modern studies are a waste of time.

Interesting viewpoint.  Are there any studies out there that confirm what you're saying, i.e. that blended wing bodies have no efficiency advantage?

@florisla: Those are done by industry (did one myself) and don't get published. The circus performed by PR and Academia is quite different from "real" engineering work.

More surface area is not always implying more friction drag, take into account that corner flows in fuselage/wing junction are more draggy than open surface. Anyhow is clear that such configuration will be, globally, more draggy, but also will allow more passengers. Key parameter here is fuel per seat and not global drag. Probably BWB should be compared with a relatively bigger airplane (same number of seats).

@TrebiaProject: When you enjoy the luxury of designing wing-fuselage intersections for a narrow band of lift coefficients, any excessive interference drag means shoddy work. And, yes, picking a flawed metric for comparisons is another of those tricks. The cleanest basis is seat-mile cost.

@PeterKämpf the fact that several airplanes have a fairing in that intersection is showing that there is business case (weight impact) of including the fairing for viscous drag reduction (potentially also supports shock wave pattern on supersonic part) in exchange of further friction drag.

Would I be correct if I assume the basic issue is that "the tube" is really hard to beat if you need to enclose usable passenger or cargo space?

@VilleNiemi: You were right to emphasize useable: This is the key. BWBs are wasteful with their space and only attractive before one looks at all the details. It's the "grass is greener on the other side of the fence" effect.

Ah yes, the dirty details would be invisible from the other side... Thanks.

@TrebiaProject.: A well done wing-fuselage intersection will use a moderate fairing because it reduces surface area. Think about it: The length of a quarter arc is less than twice the radius of the arc.

@PeterKämpf I was referring to corner flow with a bad explanation by my side.

Blended wings are more beneficial when it comes to fuel efficiency increase and noise reduction.

That has not been proven. There may be aerodynamic benefits, but unfortunately an aircraft needs to have a supporting structure as well. And if we look at a conventional configuration, we see a pressure vessel (the fuselage) supported by a lifting surface (the wing). Each has its own function and is optimised to do so:

The fuselage has a round cross section, because that is the lightest form of pressure vessel we can make. Tilt it, and it provides some lift as well.
The wing has the lowest surface area we can get away with, in order to minimise friction drag. Other factors in the optimisation equation are induced drag and structural weight.

Now combine the two functions. A blended wing or lifting body needs to be pressurised as well, how are we going to do that? Anything other than a pressure cylinder is going to be heavy, and extra weight carries a drag penalty. If we visualise a pressure cylinder inside the blended wing, we immediately start to wonder if the wing is not too large for the passenger payload required.
Start with a passenger payload, build a pressure vessel around them, provide lifting surfaces...I still come up with the conventional layout. Birds, bats and insects also have this layout, nature has not seen the advantages of a blended wing either. The answer to your question may simply be that the conventional layout is best.

"Birds, bats and insects also have this layout, nature has not seen the advantages of a blended wing either." Manta rays have a blended wing, but they operate underwater.

Like any other engineering artifact, airplanes are a product of compromises between design, mission profile, aerodynamics, flight dynamics, structures, powerplant, systems, maintenance requirements, airport requirements, etc.  As it turns out, Jack Northrop was right: Flying wings and blended wing designs are the most aerodynamically perfect solution for subsonic heavy aircraft with an added benefit of a very low radar cross section ideal for military applications.
When I was an intern at Boeing in Everett, WA back in 2000, we considered the idea of flying wings for civil transports.  While the aerodynamics make them very appealing to design and build, there are several added concerns that, combined together, deter further development of a civil transport in this configuration.
EASE OF ASSEMBLY - It is easier to assemble a semi monococque fuselage and wing box as opposed to a single, large wingbox with a cabin inside.
EMERGENCY EVACUATION - The biggest drawback to large scale flying wings is that they have less surfaces available to construct walk-in entry and egress doors, which makes it difficult to evacuate the aircraft quickly in an emergency situation.  As a yardstick, an A-380 can evacuate a total manifest of 700 people in a few minutes but the fuselage also accommodates no less than 16 emergency exits equipped with escape slides / rafts to do this.  Said number of exits are not possible on a flying wing, making it more difficult and dangerous to conduct an evacuation in an emergency.
EASE OF MAINTENANCE - Conventional airliners contain their engines and system in easily accessed compartments along the lower parts of the fuselage and wing or tailcone pylons.  On a flying wing, these systems are buried deep into the structure where they are not readily accessible.
AIRPORT INFRASTRUCTURE: Flying wings are going to have very large spans, which push the dimensional limits of existing runways, taxiways, ramp aprons, terminal gates, etc. placing limits on routes to airports which can accommodate these aircraft.  This has a direct effect on operational flexibility for the airlines looking to maximize optimal routes, large amounts of paying passenger traffic, etc.

Internal volume to be pressurized is going to be rather large. Using a cylinder inside the Blended Wing Body (BWB) as pax compartment is doable. Weight penalty, structure increases for loads involved for pressurized compartments (passengers and critical cargo).
Considering maintenance, composite structures inspections and repairs of surfaces with compound curves and critical surface fineness leaves a lot to be desired. One of those long term costs: fuel consumption. Airlines pay attention to this as it is the largest long term expense. May be a plus if the seat mile costs prove out.
Insurance. No existing comparable aircraft to compare it to. What do you think the coverage will cost? Accountants and statisticians are not fools. Historically, aircraft design has always outstripped the power plants abilities. Going to have to consider designs with existing power plants in mind. SR-71 first flew with J-75s because the J-58 wasn't there yet. Don't even consider what will be a power plant in twenty years.
Dispatch reliability needs to be taken into account for all phases of design. Mounting the engines high on top of the BWB is going to make quick engine changes let alone preflight and post-flight inspections very much down on my list of favorite things to do. Ground service infrastructure will need a lot of thought.
Where do you propose to store fuel in the structure? Next to the passenger compartment? Self loading cargo won't like that.
Marginal control surface effectiveness is going to narrow down the allowable weight and balance envelope. Movement of fuel to accommodate the movement of self loading cargo and placement of non-self loading cargo increases complexity. Not acceptable. Airlines live by the KISS Principle.
Airframe manufacturers and airlines of all types have been considering BWB aircraft for twenty years and have yet to put one in service. Ask yourself why.

Hi.  Welcome to Aviation.SE. Please edit your answer to be readable.  It is barely comprehensible to a native English speaker.  Others will really struggle.

Normal single or even twin rudder won't work with a flying wing. This is due to a length/wingspan ratio. Normal aircraft have a length/wingspan ratio of more than 1. Flying wing on the other hand have the ratio of less than 1. To solve this problem, the designer either have to enlarge the rudder or add more rudder. Up to 4 in YB-49 for example. But this enlarge or added rudder also provide added drag, thus negating the low-drag advantage the flying wing are suppose to give.
For rudderless design, the problem is yaw stability. to provide yaw control, rudderless aircraft use some sort of differential braking system. The problem is, this system doesn't provide static stability like a rudder provide. To create some semblance of yaw stability, the differential braking system have to be adjusted regularly for the entire duration of a flight. Done manually, this would've tire the pilot quickly. So a rudderless aircraft require some form of autonomous FCS to handle this. This automated system account for the extra cost and added an extra point of failure. This limit the usage of this kind of design to a military only and not the cost conscious commercial airliners.

The answers above are all very good, but I suspect that the most important reason for the lack of blended-wing passenger aircraft in service may be the simplest: flyers don't appear to like them very much.
"Boeing was going to develop a blended wing commercial aircraft in their 20 year commercial plans, but found in their initial testing of the design that passengers didn’t like it at all. The theater design of the seating just didn’t generate a favorable result and that caused Boeing to drop all commercial applications for the blended wing design, but not military applications." [emphasis added]
http://occupytheory.org/boeing-797-hoax-debunked/
All of that being said, I'd be interested to see if passengers could be induced to change their minds on that by a combination of:
1) Improved display and lighting technology in the years since this design was last tested. (Assuming the problem was claustrophobia caused by lack of windows).
2) Perpetually shrinking seat width and pitch on existing designs for economy class. If a blended-wing design allows for even a tiny bit of extra room (I realize there's analysis above to suggest that it won't, but if), budget travelers who are quite literally feeling the pinch might be won over.
3) If blended wing designs are measurably faster than their wing-and-fuselage counterparts, that's golden. If you ask a focus group participant if they like windows, they'll naturally say yes; but if you ask them to rank the value of windows vs. shaving a few hours off their flight, you might get a different response.

Could the claustrophobia problem be avoided by only seating passengers near the edges, and using the middle area for cargo (a "combi" configuration)?

The first step would be a BWB military transport.
The X48B / X48C scaled drones helped understand many issues associated with control.
The B2 bomber cost was mostly a result of early stealth materials, early large scale usage of composites. If a B2 were to be re-engineered with current stealth materials and reduced composite costs it would cost a fraction of that value to build.
The remaining substantial challenge with large BWB aircraft is pressurization.
The tube and wing shape is much easier to pressurize (wing isn't pressurized tube is one of the easiest shapes to pressurize).
BWB aircraft appears to have larger surface, but that's not true compared to an aircraft with the same cargo/pax capacity. Also what matters isn't total surface area but rather total lift vs total drag. A high lift body with less drag : lift ratio allows for higher altitude cruising which would greatly reduce fuel requirements.
BWB airliner proposed is about the same as a A380, with a much shorter length, much wider cabin, ability to carry cargo further out into the wing.
An A380 has 4 fairly large turbofan engines. A BWB the same size would have 3 similarly sized turbofans in the aft fuselage.

Welcome. Not sure it provides an answer to the question: What are the inhibiting factors for passenger airplanes?

The internal volume of a BWB is indeed larger than that of a comparable conventional configuration. But the useable internal volume (which can be pressurized without severe weight penalties) is smaller.

The first, in depth study of the Lifting Fuselage Configuration in 80 years from David Singg at the University of Toronto shows the LFC has twice the "fuel burn reduction" of the BWB/HWB compared to the tube and wing.  Vindication of the work done by Texas born Vincent Burnelli from 1921 to 1964.  Google Burnelli aircraft.
Report link...  http://oddjob.utias.utoronto.ca/~dwz/Miscellaneous/ReistZinggJofA2016.pdf
The BWB was a good step forward from the tube and wing configuration but now, the most efficient and useful design has emerged.  Even this will not guarantee production.  Just as the BWB has not been accepted because it's too radical a design, the Lifting Fuselage will take years to win acceptance.  More research to come.

Welcome to the site. A link would be good.

If talking about this presentation: it lists aerodynamic properties only, and no implications of structural weight.

This is a initial study.  I was hoping for more specifics.  I expect more detailed studies in the future.


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When the F 16 landing the flaperons are used for rolling due to the functionality as ailerons, but after touching the ground it is the same?
In landing gains the flaperons are down 20 degrees. If you have to do corrections of the bank angle on approach   then you move upward only one of the flaperons. But after touching the runaway it is the same as in the air?

After touching the ground there is no need for corrections so I imagine they act only as flaps in whatever setting is prescribed.

I don't think that the case, because all of the  aircraft moving on the runaway must be that way. I have seen that in the process of landing in cross winds the correction  is to dip one wing.

The flaperons' deflection when used als trailing edge flaps is controlled based on the landing gear handle position, the ALT FLAPS switch position, the airspeed and the mach number, but is independent of whether the aircraft is airborne or on the ground.
When the landing gear handle is placed in the DN (down) position or the ALT FLAPS switch is placed in the EXTEND position, the flaperons deflect downward. The deflection angle is 20 degrees down at airspeeds less than 240 knots. Since this is also the maximum possible downward deflection of the F-16's flaperons, there is only one way the flaperons can go when performing their function as ailerons, which is up.